It wasn’t long after Nonito Donaire won the IBF flyweight title in 2007 that his girlfriend and future wife, Rachel, asked him a simple question: “Why do you box?”

Rachel asked that question because she knew something was missing. They had met at a party in San Jose she hosted to celebrate her victory in a Taekwondo tournament. Fighter to fighter, she knew he wasn’t as happy as he should be.

“It didn’t seem like he enjoyed it,” she told The Post this week. “It seemed like he was forcing himself to get up and push himself in the gym. He was dreading practice. For me, being a fighter, you have to love what you’re doing. If you have any other reason for being in the ring besides being on top then it’s useless.”

Nevertheless, Donaire had no answer to the question, though he had just captured his first world championship after turning pro in 2001.

“It was something I did for everybody else,” Donaire said.

“I did it for my father,” he added. “I did it for anything that wasn’t me. When I started to realize that, I realized that I needed to love the sport of boxing. God has given me this talent and I’ve spent all my life in it. So why not look back and enjoy the moments and hopefully I can help a lot of people out there in the process.”

Tonight Donaire fights for his family, his fellow Filipinos and his fans when he defends his WBC/WBO bantamweight title against Argentina’s two-time world champion Omar Narvaez at the Theater at Madison Square Garden. HBO will televise.

Also featured on the card will be a 10-round bout between NABF/NABO junior lightweight champion Mikey Garcia (26-0, 22 KOs) from Oxnard, Calif., and Juan Carlos Martinez (17-12-1, 5 KOs) from Mexico.

Donaire (26-1, 18 KOs), who was born in the Philippines before moving to California at age 10, will wear pink trim on his trunks in honor of breast cancer awareness month, a cause he has embraced along with giving children hope they can succeed, just as he has.

“Now when people ask me, ‘Why do I box?’ I’ll say I box because I love the sport,” he said, “and I want to inspire other kids out there the way I was inspired to do the best I can.”

He has plans to move up to super bantamweight (122 pounds) in his next fight, where he could face Jorge Arce and eventually featherweight where he can challenge some of the bigger names like Juan Manuel Lopez. But first he must get past Narvaez (35-0-2, 19 KOs), who made 16 successful defenses of his WBO flyweight title and is moving up to bantamweight for the first time.

At age 36, Narvaez is eight years older and 4 inches shorter than Donaire. But the southpaw is an excellent counter-puncher, who likes to work the body and apply constant pressure.

“I’m looking forward to fighting a great champion like Donaire,” Narvaez said. “This is a good opportunity to show the world my boxing [skills].”

PREDICTION: Narvaez likes to wear down his opponents with constant pressure. But Donaire is bigger and stronger than anyone he has faced. Donaire by TKO in 7.

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Unbeaten super middleweights meet at Foxwoods tonight where Edwin Rodriguez (19-0, 14 KOs) takes on Will Rosinsky (14-0, eight KOs) in the main event to be televised on Showtime. Also to be televised, New York-based junior welterweight Gabriel Bracero (17-0, 3 KOs) of Puerto Rico takes on Daniel Sostre (11-4-1, four KOs).

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At the Tropicana in Atlantic City, Raymond Serrano (16-0, 8 KOs) of Philadelphia battles Angel Rios (9-7, six KOs) of The Bronx in a 10-round junior welterweight bout and New York heavyweight Vinny Maddalone (33-7, 24 KOs) takes on Mike Sheppard (20-12-1, 9 KOs) of West Virginia, also scheduled for 10 rounds.